﻿using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace Demo03
{
    class Program
    {
        static void Main(string[] args)
        {
            Console.WriteLine("请输入圆的半径：");
             double r = int.Parse(Console.ReadLine());
            double S = 3.14 * r * r;
            Console.WriteLine("圆的面积为："+S);
            Console.ReadKey();

        }
    }
}
